In general, the present invention relates to chemical telemetry using chemical sensing devices remotely located from associated pick-up and processing units for the sensing and monitoring of analytes, fluid properties such as viscosity and density, and temperature. More particularly, the invention relates to a novel remote analyte sensing apparatus, temperature sensing apparatus, and viscosity sensing apparatus, and associated new methods of sensing temperature of an environment, sensing viscosity, and sensing the presence, concentration, or absence of chemical elements and compounds (whether useful or unwanted/contaminating and in any of various states: liquid, gas, plasma, and solid), pH levels, germs (bacteria, virus, etc.), enzymes, antibodies, and so on in a number of environments such as biomedical applications (whether in vivo or in vitro), within medical test samples, food quality/inspection (whether measuring moisture within sealed packing or outside of packaging), monitoring of heavy metals found in water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), and monitoring of solid or gas manufacturing waste, etc. The new sensing apparatus and method(s) provide information about an analyte and environment utilizing magneto-elastic emissions of a sensor, or several sensor structures.
Known chemical sensing technologies generally require the operation of complex, specifically tailored sensing units, electrically connected, to monitor a target analyte. For example, Groger et al. has a FIG. 4 with a chemically sensitive film 93 positioned between coils 92 and 94 (each of which has been wrapped around a ferrite core); a FIG. 5 with eddy current probes 21 formed by chemical deposition or chemically etching a copper clad printed circuit board (PCB) substrate 11 of a conductive polymer film of polypyrrole, polythiophene or polyaniline which may be deposited directly onto the inductor array or separated by spacers; and a FIG. 6 showing a spiral-wound inductor eddy current probe 13 with a thick film ferrite core 42 deposited on (or etched on) a PCB substrate 12. The Groger et al. probe design is incorporated into an instrument that has a digital signal processor (DDS ) circuit. FIG. 9 illustrates that the probe 83 (such as that in FIG. 3 or 6) is in electrical connection with, and driven by, sinewave generator 80, preferably a direct digital signal generator, and an op amp 85 to produce a waveform output 86.
Kaiser illustrates a sensor 12, measurement circuit 10 and responder unit 16 coupled to a PCB 22 as an integrated circuit 24 (see FIGS. 1, 2A, and 2B), all contained in a housing 18. The integrated circuit 24 (FIG. 2A) is electrically connected to a sensor electrode 20 and reference electrode 21: The potential difference that develops between the electrodes 20 and 21 in relation to ion concentration, is measured to provide a pH level reading. In FIG. 2B, the sensor 12 of integrated circuit assembly 24 is a temperature sensor which is completely sealed within housing 18. FIGS. 3, 4, and 5 illustrate measurement circuit 10 embodiments: In 3 and 4, a voltage follower 44 outputs a signal proportional to the potential difference detected at sensor 12; FIG. 5 illustrates a familiar Wheatstone bridge with an AC generator 200 powered by an interrogation signal sent by interrogation unit 14. In operation (FIGS. 1 and 6), the RF transmitting and receiving circuitry 64 of interrogation unit 14, transmits an inquiry signal. Sometime thereafter, upon detecting its proper responder unit address, the responder unit 16 transmits data from the measurement circuit 10 back to interrogation unit circuitry 64.
Lewis et al. describes an analog of the mammalian olfactory system (i.e., electronic-nose) having chemiresistor elements micro-fabricated onto a micro-chip. Each sensor has at least first and second conductive leads electrically coupled to and separated by a chemically sensitive resistor (FIG. 4A-1). Each resistor has a plurality of alternating nonconductive and conductive regions transverse to the electrical path between the conductive leads. The chemiresistors are fabricated by blending a conductive material with a nonconductive organic polymer such that the electrically conductive path between the leads coupled to the resistor is interrupted by gaps of non-conductive organic polymer material. See, column 3, lines 38-50. Lewis et al. describes this as xe2x80x9celectronic noses, for detecting the presence of an analyte in a fluidxe2x80x9d (col. 8). An electronic smelling system according to Lewis et al. (col. 7) has sensor arrays in electrical communication with a measuring device for detecting resistance across each chemiresistor, a computer, a data structure of sensor array response profiles, and a comparison algorithm.
One of the applicants hereof, in conjunction with another, developed a magneto-chemical sensor comprised of a thin polymeric spacer layer made so that it swells in the presence of certain stimuli, bounded on each side by a magnetically soft thin film, as described in an article co-authored by the applicant entitled A Remotely Interrogatable Magnetochemical pH Sensor, IEEE Transactions on Magnetics, Vol. 33, No. 5, September 1997. When placed within a sinusoidal magnetic field the sensor generates a series of voltage spikes in suitably located detecting coils. The magnetic switching characteristics of the sensor are dependent upon the thickness of the sandwiched intervening polymeric spacer layer. The sandwiched xe2x80x9cchemical transduction elementxe2x80x9d of this magnetism-based technology was made of a lightly crosslinked polymer designed to swell or shrink with changes in the concentration of the species to be sensed. The magnitude of each of the voltage spikes generated by the sensor is dependent upon how much the sandwiched spacer layer has swollen in response to the given stimuli. This sensor can be used with interrogation and detection electronics commonly used in magnetic anti-theft identification marker systems.
In a subsequent structurally-modified magnetochemical sensor developed by the applicants hereof, with others (A Remotely Interrogatable Sensor for Chemical Monitoring, IEEE Transactions on Magnetics, Vol. 34, No.4, July 1998), a thin film single or array of magnetostatically coupled magnetically soft ferromagnetic thin film structure(s) is adhered to a thin polymeric layer made so that it swells or shrinks in response to a chemical analyte. The sensor is placed within a sinusoidal magnetic field and the magnetization vector of the magnetically soft coupled sensor structures periodically reverses direction generating a magnetic flux that can be remotely detected as a series of voltage spikes in pick-up coils. The four-square array is of magnetically soft thin structures bonded to a polymeric base-substrate layer with acrylate acetate (SUPERGLUE(copyright)) and baked. When the swellable base swells (low pH): the distance between the square magnetically soft structures enlarges resulting in less coupling between these structures. If immersed in high pH: this base shrinks as does the distance between structures resulting in a larger voltage signal.
Anderson, III et al. discloses a marker 16 (FIG. 5) formed of a strip 18 of a magnetostrictive, ferromagnetic material adapted, when armed in its activated mode, to resonate mechanically at a frequency within the range of the incident magnetic field. A hard ferromagnetic element 44 disposed adjacent to the strip 18 is adapted, upon being magnetized, to magnetically bias the strip 18 and thereby arm it to resonate at that frequency. An oscillator provides an AC magnetic field within interrogation zone 12 to mechanically resonate a magnetostrictive strip 18, which has first been armed by a magnetized hard ferromagnetic element 44, upon exposure to this AC magnetic field. The sole object of Anderson, III et al. EAS marker is to detect the presence between coil units 22 and 24 (interrogation zone 12) of an xe2x80x9carmed/activatedxe2x80x9d marker 16. In the event an activated marker 16 secured to a retail article is detected within zone 12, an alarm will sound. A deactivator system 38, electrically connected to a cash register, can be used to deactivate the marker. FIG. 3 graphically illustrates that, for the Anderson, III et al. marker, the voltage induced by mechanical energy exchange peaks (just over 12 volts) at fr, the resonant frequency, and is a minimum at fa (anti-resonant frequency).
Humphrey and, another reference, Humphrey et al. disclose harmonic type electronic article surveillance (EAS) markers which include a thin strip or wire of magnetic material that responds to an alternativing interrogation signal by generating a signal pulse that is rich in high harmonics of the interrogation signal.
Winkler et al. relates to electronic article surveillance (EAS) anti-theft systems, which operate by detecting mechanical resonances of magnetostrictive elements made of amorphous metallic glass METGLAS(copyright) 2826 MB, to prevent or deter theft of merchandise from retail establishments. FIG. 8 illustrates a magnetomechanical system for detecting unauthorized passage through an interrogation zone of an article of merchandise. In response to an interrogation signal generated by energizing circuit 201, the interrogating coil 206 generates an interrogating magnetic field, which in turn excites the integrated marker portion 12 of the article of merchandise 10 into mechanical resonance. During the period that the circuit 202 is activated, and if an active marker is present in the interrogating magnetic field, such marker will generate in the receiver coil 207 a signal at the frequency of mechanical resonance of the marker. This signal is sensed by a receiver which responds to the sensed signal by generating a signal to an indicator to generate an alarm.
Copeland discloses an article surveillance system having two (first and second) diverse magnetic materials with diverse timewise responsivity to the magnetic field in the control zone. The first is a tag or marker material having principal responsivity to the magnetic field at or near the zero-crossover current of the time-varying signal; and the second is a shielding material with a principal responsivity to the magnetic field at or near the peaks of the positive and negative excursions of the time-varying signal (i.e., selected to function as a shield). A method aspect is also explained.
Schrott, et al. describes a multibit bimorph magnetic ID tag for attachment to, and identification of, an object. The tag has one or more bimorphs comprised of a thin strip of a magnetostrictive material attached to a thicker bar 21 of hard magnetic material. A shipping pallet, package, or product is tagged with the bimorph for later product identification. The Schrott, et al. ID tag is excited using either magnetic or acoustic fields (ranging in frequency up to 50 to 100 kHz, and preferably 5-50 kHz) tuned to the resonance of the bimorph tags. The bar 21 of hard magnetic material of the bimorph cantilever is several times (e.g. 5) thicker, for the same length, than the magnetostrictive strip, in order to have the bimorph vibrate at frequencies determined by the bar dimensions. The excitation induces strain in the bimorph which causes mechanical vibrations in the bimorph that are sensed acoustically or magnetically, giving rise to a predetermined code tied directly to whether the ID tag is resonating at the interrogation frequency (ON), or it is not (OFF). A device for detecting the output of the tag, along with a device 8 for decoding the output from the detecting means thereby, are also needed. Schrott et al. indicates that a multibit tag could be programmed to generate a binary or other suitable code. In the binary code case, a certain frequency of an array of cantilevers can be assigned a value of xe2x80x9czeroxe2x80x9d or xe2x80x9conexe2x80x9d and, if absent, it can take the opposite value. The Schrott, et al. ID tag is limited to coded (zeros and ones) identification of the object. If, in operation, a Schrott, et al. ID tag""s resonant frequency (predetermined by size/materials) is not xe2x80x9chitxe2x80x9d during interrogation due to some unexpected event/external factor (such as, its resonant frequency is changed due to a temperature swing, or due to reaction of the ID tag with a surrounding fluid), no response will be detected and an incorrect output code will result, thus, destroying the Schrott, et al. ID tag""s function.
As one can appreciate, unlike the instant invention, known electrical system chemical sensors available for use are dependent upon direct electrical connection between the sensing unit and an input AC-energy or sinewave generator, and output measurement circuitry having an associated directly-connected computer processor. Although chemical analysis is being done using laser reflection, such laser analysis requires that a fiber optic cable or light beam enter the environment being tested; making laser analysis difficult (if not impossible) within opaque packaging or piping, in vivo, and so on, where no line-of-sight for the laser beam can be reliably maintained. These known sensors have been designed for specifically-targeted test environments. The particular magnetochemical sensors (described above, see A Remotely Interrogatable Magnetochemical pH Sensor, IEEE Transactions on Magnetics, Vol. 33, No. 5, September 1997) developed in collaboration with the applicant hereof, have been designed with a crosslinked polymer chemical transduction element adhered to a magnetically soft ferromagentic thin film structure to specifically respond to a surrounding sinusoidal magnetic field by detecting changes in magnetic flux (as voltage spikes). And, known magnetic markers developed for use in EAS simply register the presence or absence of the magnetic marker, as sensed within a region, based upon the EAS marker""s response to a magnetic field produced by a magnetic field transmitter. Furthermore, many of the currently available chemical sensor systems rely on proper orientation of the sensor within the interrogation field. This is undesirable, as it is often very difficult to guarantee a particular sensor orientation within most test environments (example, in vivo testing).
Viscosity, defined as the resistance that a gaseous or liquid (i.e., a fluid) system offers to flow when it is subjected to a shear stress, is generally measured by cumbersome meters. Mathematically, the shear stress (xcfx84) of a fluid near a wall is given by:                     τ        =                  μ          ⁢                                    ⅆ              V                                      ⅆ              y                                                          [        1        ]            
where xcexc is the dynamic viscosity and dV/dy is the time rate of strain (also called the velocity gradient). As one can see, dynamic viscosity xcexc (having units Nxc2x7s/m2) is the ratio of shear stress to velocity gradient. Measuring viscosity, especially of a fluid in motion, is no simple task.
Therefore, a versatile robust sensor apparatus and method are needed for obtaining information about an analyte or an environment (including one with a fluid therewithin) through remote query, without direct electrical hard-wire connection and without the need to ensure the sensor""s orientation in order to provide such information, in various diverse test samples/environments.
The new compact analyte, temperature, and viscosity sensing apparatuses, and associated methods of sensing, described herein, are designed for operation within a wide range of tests and testing environments whether one-time, periodic, or continuous on-going monitoring of a particular analyte or environment is desired. The innovative sensing apparatus and method use a base magnetostrictive element to which a chemically, thermally, or frictionally responsive layer/element may be adhered to create a unique analyte recognition, temperature or viscosity sensing structure and technique that can utilize either: (a) a ratio of magneto-elastic energy emission measurements of the sensor structure taken at two different magneto-elastic listening frequencies (preferably around a fundamental or harmonic resonant frequency), or (b) at least two successive magneto-elastic emission intensity values taken over a range of successive interrogation frequencies (preferably including a fundamental or harmonic resonant frequency), to identify a fluid viscosity or temperature, or detect the presence, absence, and/or measure minute, and larger, amounts of an analyte in gas, plasma, liquid, or solid phase. This being done without requiring sophisticated equipment and without taking up a great deal of space. Furthermore, this new sensor structure can be installed/positioned and removed with relative ease and without substantial disruption of the test sample or test environment. If need be, the sensor may be fabricated as a micro-circuit for use in vitro, in vivo, within small-sized sealed packaging or medical test samples (e.g., a test tube), and so on. A micro-sensor can be used where space is limited and/or it is desired that the tiny sensor be positioned further into the interior of the sample or environment being tested/monitored. And, whether or not built on a larger scale, the novel sensor can be used for sensing within buildings or other open space to measure contaminant gas, in waterways to measure heavy-metal contamination, and so on.
Simply defined, xe2x80x9cmagnetostrictionxe2x80x9d is the phenomena whereby a material will change shape (dimensions) in the presence of an external magnetic field. This effect is brought about by the reordering of the magnetic dipoles within the material. Since the atoms in a magnetostrictive material are not, for all practical purposes, perfectly spherical (they""re shaped more like tiny ellipsoids) the reordering of the dipoles causes an elongation (or contraction depending on the mode of reorientation) of the lattice which leads to a macroscopic shape change in the material. There is a xe2x80x9creverse magnetostrictive effectxe2x80x9d, called the Villari effect: When an external stress is applied to a magnetostrictive material, a strain develops within the material which induces a surrounding magnetic field. Known magnetostrictive materials include alloys of iron (Fe), cobalt (Co), samarium (Sm), yttrium (Y), gadolinium (Gd), terbium (TB), and dysprosium (Dy).
The new analyte, temperature, and viscosity sensing apparatuses and methods were developed to utilize space more efficiently while at the same time provide sufficient sensitivity. As can be appreciated, in the spirit and scope of these design goals and as described further, the sensor structures can be fabricated from micro-components or can be built on a larger scale and formed into many different shapes and layers; and several such sensors can be incorporated into an array to provide a package of sensing information.
It is a primary object of this invention to provide apparatuses and associated methods for detecting the presence, absence, and/or measuring the amount of an analyte, as well as sensing the temperature of an environment (whether or not a fluid is within the environment) and sensing fluid viscosity, mass density or other such property. A sensing structure (sensor) is used that has a base magnetostrictive element to which a chemically, thermally, or frictionally responsive layer/element (as the case may be) may be adhered. It is also an object of this invention that such apparatuses and methods utilize either: (a) a ratio of magneto-elastic energy emission measurements of the sensor structure taken at two different magneto-elastic listening frequencies, or (b) at least two successive magneto-elastic emission intensity values taken over a range of successive interrogation frequencies, to perform the sensing/detecting. It is also an object of this invention to provide such a sensing structure that needs no direct hard-wire connection to its field generating coil or magneto-elastic emission receiving coil, but rather, is remotely located for sensing.
The advantages of providing the new analyte and temperature sensing apparatuses and associated new methods, as described herein, are as follows:
(a) The invention can be used for one-time (whether disposable) operation, periodic, or continuous on-going monitoring of a particular analyte or environment;
(b)Versatilityxe2x80x94The invention can be used for operation within a wide range of testing environments such as biomedical applications (whether in vivo or in vitro), within medical test samples, food quality/inspection (within or outside of sealed packing), monitoring of contaminants in water (groundwater, treated water, or wastewater flowing in natural waterways, canals, or pipes), and monitoring of solid or gas manufacturing waste;
(c) Simplicity of usexe2x80x94The new sensor structure can be installed/positioned and removed with relative ease and without substantial disruption of a test sample/environment;
(d) Structural design flexibilityxe2x80x94the sensor may be formed into many different shapes and may be fabricated as a micro-circuit for use where space is limited and/or the tiny sensor must be positioned further into the interior of a sample or environment being tested/monitored;
(e) Structural design for sensing speedxe2x80x94If a layer of chemically or thermally responsive material is adhered to the magnetostrictive base, that layer can be shaped to maximize the speed at which the material responds, allowing the sensor to provide useful information at a faster rate;
(f) Several sensors may be positioned, each at a different location within a large test environment, to sample each of the different locations, simultaneously or sequentially;
(g) Several sensors may be incorporated into an array to provide a package of sensing information about an environment, such as, analyte composition, a fluid viscosity or mass density measurement, and temperature of the environment in which the analyte and fluid are found;
(h) Receiving unit design flexibilityxe2x80x94One unit may be built with the capacity to receive acoustic emissions (elastic nonelectromagnetic waves that can have a frequency up into the gigahertz, GHz, range) as well as electromagnetic emissions emanating from the sensor, or separate acoustic wave and electromagnetic wave receiving units may be used;
(i) Apparatus design simplicityxe2x80x94Reducing the number and size of components required to build an analyte, viscosity (or other fluid property), or temperature sensing apparatus can reduce overall fabrication costs and add to ease of operation; and
(j) Sensor materials and size can be chosen to make one-time, disposable use economically feasible.
Briefly described, the invention includes an analyte sensing apparatus for operative arrangement within a time-varying magnetic field, comprising a sensor having an outer surface of a material that is chemically responsive to the analyte, adhered to a base magnetostrictive element, and a receiver to measure a first and second value for magneto-elastic emission intensity of the sensor taken at, respectively, a first and second interrogation frequency. A change in mass, if any, of the sensor (or a change in its material stiffness) due to the chemical responsiveness is identified using a ratio of the first and second values. The first interrogation frequency is preferably less than the sensor""s magneto-elastic resonant frequency (or harmonic thereof) by an interval (xcex94f) from the magneto-elastic resonant frequency, and the second interrogation frequency is preferably greater than the resonant frequency (or harmonic thereof) by approximately the interval (xcex94f); xcex94ƒ may be a value between 0.001% and 20% (and, perhaps, up to 40%) times the resonant frequency ƒ0 (or a harmonic).
Also described is an analyte sensing apparatus, comprising this sensor and a receiver to measure a plurality of successive values for magneto-elastic emission intensity of the sensor taken over an operating range of successive interrogation frequencies to identify a magneto-elastic resonant frequency (or harmonic thereof) value for the sensor; whereby a change in mass, if any, of this sensor due to the chemical responsiveness is identified by using the magneto-elastic resonant frequency value. The resonant frequency value identified generally corresponds with a relative maximum of the successive values for emission intensity measured. This range of successive interrogation frequencies could be chosen as a range between 79% and 121% of the resonant frequency (or harmonic) for the sensor.
Also characterized herein, is a temperature sensing apparatus for operative arrangement within an environment having a time-varying magnetic field. This apparatus comprises: a sensor having a base magnetostrictive element; and a receiver to measure a first and second value for magneto-elastic emission intensity of the sensor taken at, respectively, a first and second interrogation frequency; whereby temperature of the environment is identified using a ratio of the first and second values. As before, the first interrogation frequency is preferably less than the sensor""s magneto-elastic resonant frequency (or harmonic thereof) by an interval (xcex94ƒ), and the second interrogation frequency is preferably greater than the resonant frequency (or harmonic thereof). A pre-correlation made between a series of emission intensity ratio values taken for the sensor and a corresponding series of temperature values for the sensor, is used for the identification of the environment""s temperature. An outer surface of a material (such as a polymer) that is thermally responsive to the environment can be adhered to the base element.
Also characterized herein, is a temperature sensing apparatus comprising: a sensor having a base magnetostrictive element; and a receiver to measure a plurality of successive values for magneto-elastic emission intensity of the sensor taken over an operating range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the sensor; whereby temperature of the environment is identified by using the resonant frequency value.
Additionally, the temperature sensing apparatuses may incorporate a sensor with a thermally responsive thin outer layer having a value for coefficient of thermal expansion that is greater than a coefficient of thermal expansion value for its base element. The base element may be sandwiched between two such layers (e.g., out of antimonial lead or zinc).
Also characterized herein, is an apparatus for sensing at least one property of a fluid for operative arrangement within a time-varying magnetic field, comprising: a sensor having a base magnetostrictive element, and a receiver to measure either (a) a first and second value for magneto-elastic emission intensity of the sensor taken at, respectively, a first and second interrogation frequency, whereby the fluid property is identified using a ratio of these first and second values, or (b) a plurality of successive values for magneto-elastic emission intensity of the sensor taken over an operating range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the sensor, whereby the fluid property is identified by using this magneto-elastic resonant frequency value. As before, the first interrogation frequency is preferably less than the sensor""s magneto-elastic resonant frequency (or harmonic thereof) by an interval (xcex94ƒ), and the second interrogation frequency is preferably greater than the resonant frequency (or harmonic thereof). The fluid property sensor, operating as a viscosity sensor, may further comprise an outer surface that is frictionally responsive to the fluid being sensed; and a fixture to slidably retain the sensor can be incorporated with this viscosity sensing apparatus.
The magneto-elastic emission may be an acoustic emission, an electromagnetic emission, or other detectable wave type emitted by the sensor. And, the type of receiver used (such as an electroacoustic device containing a transducer or an electromagnetic pick-up coil) will depend upon the type of magneto-elastic emission being received. If electromagnetic emission intensity is measured by the receiver, one may choose to perform such measurement after the time-varying magnetic interrogation field has been turned off. The magnetostrictive element can be made of an alloy of an element selected from: iron, cobalt, samarium, yttrium, gadolinium, terbium, dysprosium, and so on. For the analyte and viscosity sensors, it is preferred that an alloy is chosen having material properties that remain generally unchanged over a preselected range of operating temperatures.
There are additional features that further distinguish the apparatuses of the invention from known sensing system designs. The chemically responsive outer surface can be that of many different types of materials, such as (note that the particular mechanism of chemical responsiveness is not critical): A chemically receptive polymer layer having a plurality of microspheres; a chemically receptive porous polymer layer (into which at least a portion of the analyte can diffuse); a sorbent polymer film selected from the group of a poly(isobutylene), ethylene-propylene rubber, poly(isoprene), and poly(butadiene) film; an outer polymer hydrogel monolayer reactive to electrostatic forces of subatomic particles within the analyte; a chemically receptive polymer layer (from which there is a loss of matter); a zeolite layer which can interact with at least a portion of subatomic particles in the analyte to cause a gain in mass of the zeolite layer; and so on. The frictionally responsive layer can be that of a layer of latex, and such, to increase surface roughness.
Furthermore, a magnetizable magnetically hard element can be positioned in proximity to the analyte, viscosity, or temperature sensor to act as an ON-OFF switch; or, such a magnetized (activated) magnetically hard element could be positioned to provide a DC bias magnetic field superimposed onto the time-varying field. In operation the ON-OFF switch, once activated to support an external stray magnetic field, would reversibly turn the sensor structure off. In the event a xe2x80x9cpackagexe2x80x9d of different types of sensing information about one environment is sought, more than one sensor may be maintained in an ordered array, for example, by being organized to extend along or contained within chambers of a support member. Each sensor within the array may have a distinct operating range, allowing the receiver to distinguish emissions received from each separate sensor. Thus, the separate types of sensing information can be obtained, tracked and computed. A magnetically hard element can, likewise, be organized along or within the support member (although it need not be attached thereto) in proximity to a dedicated sensor structure for activation to contribute a DC bias field to that surrounding the sensor.
The invention also includes a method of sensing an analyte with a sensor having a chemically responsive outer surface adhered to a base magnetostrictive element, the sensor having a magneto-elastic resonant frequency, comprising the steps of: applying a time-varying magnetic field; measuring a first and second value for magneto-elastic emission intensity of the sensor with a receiver operating at, respectively, a first and second interrogation frequency; and using a ratio of the first and second values to identify a change in mass, if any, of the sensor due to the chemical responsiveness. As before, the first interrogation frequency is preferably less than the sensor""s magneto-elastic resonant frequency (or harmonic thereof) by an interval (xcex94ƒ) from the magneto-elastic resonant frequency, and the second interrogation frequency is preferably greater than the resonant frequency (or harmonic thereof) by an interval (xcex94ƒ): xcex94ƒ can be a value between 0.00% and 20% (and up to 40%) times the resonant frequency ƒ0 (or a harmonic). The method can also include, prior to the step of using a ratio, the step of pre-correlating a series of emission intensity ratio values taken for the sensor and a corresponding series of mass change values for the sensor (this step of pre-correlating can be used to identify a change in mass, if any). If there is no mass change, a change in material stiffness of the sensor due to the chemical responsiveness may be identified. To further accomplish the sensing of the analyte, the step of applying a known relationship between the change in mass (or change in material stiffness, as the case may be) and the analyte (or material property thereof), can be included.
Also characterized herein, is a method of sensing an analyte with a sensor having a chemically responsive outer surface adhered to a base magnetostrictive element, comprising the steps of: applying a time-varying magnetic field; measuring a plurality of successive values for magneto-elastic emission intensity of the sensor with a receiver operating over a range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the sensor; pre-correlating a series of resonant frequency values taken for the sensor and a corresponding series of mass change values for the sensor; and using the magneto-elastic resonant frequency value identified and the step of pre-correlating to identify a change in mass, if any, of the sensor due to the chemical responsiveness. This range of successive interrogation frequencies could be chosen as a range somewhere between 79% and 121% of the resonant frequency for the sensor.
Additional novel methods of the invention are characterized herein. One being a method of sensing a temperature of an environment with a sensor having a base magnetostrictive element, comprising the steps of: applying a time-varying magnetic field; measuring a first and second value for magneto-elastic emission intensity of the sensor with a receiver operating at, respectively, a first and second interrogation frequency; and using a ratio of the first and second values to identify the temperature. Another method of sensing a temperature of an environment with a sensor having a base magnetostrictive element, includes the steps of: applying a time-varying magnetic field; measuring a plurality of successive values for magneto-elastic emission intensity of the sensor with a receiver operating over a range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the sensor; pre-correlating a series of resonant frequency values taken for the sensor and a corresponding series of temperature values for the sensor; and using the magneto-elastic resonant frequency value identified and the step of pre-correlating to identify the temperature.
Further characterizations of the method of the invention, include a method of sensing at least one property (such as viscosity or mass density) of a fluid with a sensor having a base magnetostrictive element, comprising the steps of applying a time-varying magnetic field, and either:
(a) measuring a first and second value for magneto-elastic emission intensity of the sensor with a receiver operating at, respectively, a first and second interrogation frequency, and using a ratio of the first and second values to identify the fluid""s property; or
(b) measuring a plurality of successive values for magneto-elastic emission intensity of the sensor with a receiver operating over a range of successive interrogation frequencies to identify a magneto-elastic resonant frequency (or harmonic thereof) value for the sensor, pre-correlating a series of resonant frequency values taken for the sensor and a corresponding series of viscosity values for the sensor, and using the resonant frequency (or harmonic) value and the pre-correlation to identify the property.
There are additional features that further distinguish the methods of the invention from known sensing system and method designs. In the event a xe2x80x9cpackagexe2x80x9d of different types of sensing information about one environment is sought, one can add the step of measuring a third and fourth value for magneto-elastic emission intensity of a second sensor with the receiver operating at, respectively, a third and fourth interrogation frequency; or one could add the step of measuring a second plurality of successive values for magneto-elastic emission intensity of a second sensor with said receiver operating over a second range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the second sensor. If at least three types of sensing information is sought, one could further add the step of measuring a third plurality of successive values for magneto-elastic emission intensity of a third sensor with the receiver operating over a third range of successive interrogation frequencies to identify a magneto-elastic resonant frequency value for the third sensor, and so on. Each of the sensors may extend along, or be contained within a chamber of, a support member in an ordered array, or each could be immersed for free independent movement throughout the environment. A dedicated DC bias magnetic field may be desirable for each, or any one of, the sensors in the array.